Formulary

How a formulary turns evidence into medicine coverage

A formulary is a governed list of medicines that a health plan, health system, hospital, or public programme has selected for coverage or routine use under stated conditions. It connects clinical evidence, comparative value, prices, contracting, prescribing policy, and patient cost sharing. This page explains how medicines enter and move within a formulary, how access rules operate, and how to judge whether the resulting design improves health, affordability, and equity.

A formulary is more than a list

A medicine's presence on a formulary does not necessarily mean unrestricted access or the same coverage for every patient. The record can specify indication, line of therapy, prescriber type, care setting, quantity, age, prior treatment, monitoring, and member payment. A complete formulary therefore combines product status with the rules governing actual use.

Formulary element	What it determines	Example
Inclusion status	Whether the medicine is routinely covered or available	Listed, non-formulary, or excluded
Tier	The member cost-sharing or preference level	Preferred generic or non-preferred brand
Clinical criteria	The patients and circumstances eligible for use	Confirmed diagnosis or biomarker status
Utilisation management	The approval steps or limits applied	Prior authorisation, step therapy, or quantity limit
Site and channel	Where or how the medicine is supplied	Retail, specialty pharmacy, hospital, or home infusion
Exceptions process	How access outside standard rules is considered	Medical exception or urgent review

Formularies operate in different settings

The term formulary is used across organisations with different legal duties and objectives. A hospital formulary may guide procurement and prescribing within one institution, while an insurer's formulary defines pharmacy-benefit coverage and member cost sharing. National or regional formularies may support standardisation, essential-medicines policy, reimbursement, or prescribing guidance.

The setting should always be stated because the decision authority, population, payment rules, and consequences of non-formulary status differ. A medicine unavailable for routine hospital stocking may still be obtainable through an exceptional-use process, whereas an insurance exclusion may leave the patient responsible for the full price.

Selection begins with a defined decision question

Formulary review should specify the medicine, indication, target population, comparators, outcomes, setting, and decision date. A broad review of a molecule can conceal major differences across indications, formulations, doses, and patient groups. The committee should also state whether it is deciding inclusion, preferred position, restrictions, substitution, or removal.

Important questions include:

• Does the medicine provide clinically meaningful benefit over relevant alternatives?
• What harms, monitoring requirements, and implementation risks accompany its use?
• Which patients are most likely to benefit or experience harm?
• How certain and transferable is the evidence?
• What are the acquisition cost and total consequences for healthcare spending?
• Could the coverage rule create avoidable access barriers or inequities?

Pharmacy and therapeutics governance

A pharmacy and therapeutics committee, or an equivalent multidisciplinary body, commonly oversees formulary decisions. Credible governance combines clinical, pharmacy, methodological, economic, operational, and patient perspectives while managing conflicts of interest. The committee's reasons should be documented well enough to support consistent decisions and future review.

A robust process includes:

• Published membership, remit, quorum, and voting rules.
• Conflict-of-interest declaration and management.
• Standard evidence requirements and appraisal templates.
• Patient and clinician input appropriate to the decision.
• Written decisions, reasons, conditions, and review dates.
• Appeals, exceptions, and reconsideration routes.
• Version control and timely communication of changes.

Clinical evidence establishes comparative benefit and harm

Formulary assessment should compare patient-relevant benefits and harms with the alternatives actually used in the health system. Regulatory approval establishes that a medicine may be marketed for an authorised use; it does not determine its preferred formulary position. Indirect comparisons, surrogate endpoints, single-arm evidence, and short follow-up require explicit uncertainty assessment.

The evidence review should address:

• Relevant clinical outcomes, adverse events, and health-related quality of life.
• Comparative effectiveness rather than placebo evidence alone when active alternatives exist.
• Applicability to the covered population and routine practice.
• Treatment duration, adherence, persistence, and discontinuation.
• Subgroup effects and the credibility of effect modification.
• Evidence maturity and the need for reassessment.

Economic evidence considers more than acquisition price

The lowest unit price does not necessarily produce the lowest total cost or best value. Treatment can alter monitoring, administration, hospitalisation, adverse-event management, disease progression, productivity, and future care. Economic evidence should match the organisation's perspective and distinguish cost-effectiveness, affordability, and budget impact.

A simplified expected net treatment cost is:

$$ Net\ treatment\ cost = Acquisition + Administration + Monitoring + Adverse\ event\ costs - Avoided\ healthcare\ costs $$

This calculation does not by itself establish value because health outcomes must also be considered. Contract terms, rebates, and confidential discounts should be applied consistently and their uncertainty or restrictions disclosed to authorised decision makers.

Budget impact depends on uptake and displacement

Budget impact estimates how formulary adoption changes expenditure for a defined payer or system over a specified period. It depends on the eligible population, treatment mix, uptake, switching, persistence, price, implementation, and displaced therapies. A low per-patient incremental cost can still create a large budget impact when the eligible population is large.

For period (t), a simplified formulation is:

$$ Budget\ impact_t = Cost_{new\ mix,t} - Cost_{current\ mix,t} $$

Scenarios should test uptake, negotiated prices, eligibility, treatment duration, and substitution. The analysis should not count a rebate without also applying its qualifying conditions and timing.

Tiering changes price signals to patients

Tiered formularies assign different copayments or coinsurance to encourage use of preferred medicines. Tiers may distinguish generics, preferred brands, non-preferred brands, and specialty medicines, but structures vary across plans. A higher tier can reduce plan spending while increasing non-initiation, poor adherence, or financial hardship for patients.

Tier placement should be interpreted with:

• The exact copayment or coinsurance rule.
• Whether a deductible applies before tier cost sharing.
• The medicine's allowed or negotiated price.
• Accumulator and out-of-pocket maximum rules.
• Availability of clinically appropriate lower-tier alternatives.
• Exceptions that allow a lower cost-sharing level when alternatives are unsuitable.

Prior authorisation verifies coverage criteria

Prior authorisation requires approval before the plan pays for a medicine. It can support evidence-based use, confirm diagnosis, manage safety, or steer treatment, but it can also delay initiation and create workload. Criteria should be clinically justified, transparent, current, and no more burdensome than necessary.

Evaluation should measure approval, denial, turnaround, abandonment, appeal, overturn, health outcomes, and administrative cost. Approval rates alone are insufficient because patients may never complete the request or may experience clinically important delay.

Step therapy sets a treatment sequence

Step therapy generally requires trial of one or more preferred treatments before coverage of another medicine. A sequence may be reasonable when alternatives have comparable expected benefit and lower cost or better-established safety. It becomes problematic when earlier steps are contraindicated, previously ineffective, poorly tolerated, or inappropriate for the patient's disease severity.

An accessible exception process should address previous treatment history, contraindication, expected harm, clinical urgency, and risk of irreversible deterioration. The sequence and exception criteria should be reviewed as evidence, prices, and standards of care change.

Quantity limits and supply rules affect continuity

Quantity limits can align dispensing with approved dose, reduce waste, manage safety, or prevent misuse. They can also interrupt therapy when dose titration, loading schedules, travel, lost medication, or clinical need falls outside the default. Specialty-pharmacy and limited-distribution requirements can introduce additional coordination and delivery risks.

Rules should specify dose assumptions, refill timing, overrides, emergency supply, transition arrangements, and responsibility for resolving failed claims. Monitoring should identify gaps in treatment and disproportionate burden for patients with complex needs.

Non-formulary status and exclusion are not identical

A non-formulary medicine may remain available through an exception, higher cost sharing, or individual review. An excluded medicine may receive no plan payment unless a legal or contractual protection applies. Clear terminology is essential because patients and clinicians need to know whether access is difficult, expensive, conditional, or unavailable.

The formulary should state the pathway for medical exceptions, urgent requests, appeals, independent review, and continuity during a decision. Instructions should be usable without specialist knowledge or unnecessary documentation.

Therapeutic interchange and substitution need safeguards

Therapeutic interchange replaces a prescribed medicine with a different but clinically comparable medicine under an approved protocol. Generic or biosimilar substitution may involve a product with the same active substance or a regulated comparable biological product, depending on jurisdiction. These practices should not be conflated because evidence standards, authority, and patient considerations differ.

Protocols should address clinical equivalence, contraindications, narrow therapeutic index, device differences, immunogenicity, monitoring, prescriber notification, patient communication, and opt-out conditions. Savings should be evaluated alongside continuity, adherence, and outcomes.

Rebates can change formulary position

Manufacturers and payers may agree rebates, discounts, price-volume arrangements, or outcomes-based contracts. Net price can affect preferred status, but opaque rebates can create incentives that do not align with patient cost sharing or total system value. The relevant decision is based on the complete contract and expected consequences, not the published list price alone.

Reviewers should examine:

• The effective net price and uncertainty about contract performance.
• Whether member cost sharing is based on list or net price.
• Minimum share, volume, exclusivity, or placement conditions.
• Administrative and data requirements.
• Consequences for competing products and future market entry.
• Whether short-term savings could increase total costs or reduce appropriate access.

Formularies influence adherence and outcomes

Tier changes, restrictions, and product switches can affect whether treatment is started, taken consistently, and continued. These behavioural effects can alter clinical outcomes and downstream healthcare use. Post-decision monitoring should therefore connect formulary changes to patient pathways rather than reporting pharmacy expenditure alone.

Useful measures include:

• Prescription initiation and abandonment.
• Time from prescription to treatment.
• Adherence, persistence, switching, and discontinuation.
• Disease control, adverse events, hospitalisation, and emergency care.
• Member spending and financial hardship.
• Clinician and patient administrative burden.
• Outcomes across socioeconomic, racial, geographic, disability, and clinical groups.

Equity requires more than uniform rules

The same formulary rule can have different effects depending on income, health literacy, language, digital access, transport, clinician capacity, and disease burden. Uniform cost sharing or documentation can therefore create unequal effective access. Equity assessment should identify who bears the financial and administrative burden and whose treatment is delayed or abandoned.

Potential safeguards include reduced cost sharing for high-value treatment, accessible exception processes, multilingual support, alternative submission routes, continuity protections, and monitoring by relevant subgroup. Safeguards should solve demonstrated barriers without making the underlying criteria less clinically sound.

Closed and open formularies involve different trade-offs

An open formulary generally covers a broad range of medicines, often with different preference levels, while a closed formulary limits routine coverage to selected products. Closed designs can strengthen purchasing leverage and consistency but require reliable exceptions when covered options are unsuitable. Open designs can preserve choice while weakening price negotiation and exposing patients to high cost sharing.

Neither design is inherently better. Credibility depends on evidence-based selection, clinically adequate alternatives, transparent rules, effective exceptions, and observed effects on health and access.

Formularies must change with evidence and practice

Formularies are living governance tools. New trials, safety warnings, shortages, generic or biosimilar entry, price changes, new indications, utilisation patterns, and real-world outcomes can alter a medicine's preferred position. Review schedules should reflect the importance and volatility of the evidence rather than relying only on annual updates.

Triggers for reassessment include:

• New comparative effectiveness or safety evidence.
• Regulatory restriction, withdrawal, or expanded indication.
• Loss of exclusivity or entry of a lower-cost alternative.
• Supply disruption or persistent shortage.
• Unexpected uptake, spending, denial, or abandonment.
• Evidence that criteria cause harm, inequity, or avoidable burden.
• Failure of a managed agreement or outcomes condition.

Evaluating a formulary change

A formulary change should be evaluated against a defined counterfactual and across the complete care pathway. Before-and-after spending comparisons can be misleading when prices, populations, disease severity, or other policies also change. Stronger designs use appropriate comparison groups, segmented time trends, or patient-level adjustment when feasible.

1. Specify the change. Record products, tiers, restrictions, dates, populations, and transition arrangements.
2. Map the expected pathway. Show how the change could affect prescribing, approval, initiation, adherence, outcomes, and spending.
3. Pre-specify balanced measures. Include clinical outcomes, access, burden, equity, and total costs.
4. Choose a credible comparator. Address concurrent changes, enrolment, and differences in patient risk.
5. Monitor early warning signals. Track delays, abandonment, appeals, acute care, and shortages during implementation.
6. Revise when necessary. Change criteria, tiering, communication, or exceptions when harms outweigh intended gains.

Common misunderstandings

A formulary can appear simple because it is often displayed as a searchable list. The policy behind each listing is what determines actual coverage and behaviour. The following distinctions prevent an incomplete or misleading interpretation.

• Formulary inclusion does not mean unrestricted or zero-cost access.
• Non-formulary status does not always mean absolute exclusion.
• A preferred tier does not prove clinical superiority.
• The lowest acquisition price does not necessarily minimise total cost.
• Prior authorisation approval rates do not capture abandonment or delay.
• A rebate does not automatically reduce the price paid by the patient.
• A formulary is not equivalent to a clinical guideline, although the two can inform each other.
• Lower pharmacy spending does not demonstrate better value if health outcomes or other costs worsen.

Reporting a formulary transparently

A usable formulary should allow patients, clinicians, reviewers, and automated systems to determine the current coverage rule for a specific medicine and circumstance. Public-facing information should be plain enough for care decisions, while governance records preserve the underlying evidence and rationale. Effective dates and version history prevent reliance on obsolete rules.

• State the medicine, formulation, indication, tier, and coverage status.
• State all prior authorisation, step therapy, quantity, prescriber, site, and channel requirements.
• Provide cost-sharing information or a reliable route to member-specific estimates.
• Explain exceptions, urgent review, appeals, and continuity protections.
• Identify the effective date, next review, and changes from the previous version.
• Document evidence, economic analysis, conflicts, committee decision, and rationale.
• Report monitoring results for access, health, spending, burden, and equity.

The decision standard

A high-quality formulary makes clinically appropriate medicines accessible while using pooled resources responsibly and protecting patients from avoidable cost and administrative barriers. Its success is not shown by the length of the list or the size of a pharmacy saving. The correct test is whether the complete set of selections, tiers, conditions, prices, exceptions, and monitoring produces better value, safe access, and equitable outcomes in the population it serves.