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TL;DRAut idem, Latin for "or the same", is the rule under §129 Abs. 1 SGB V by which a German pharmacy dispenses a wirkstoffgleiches (same active ingredient), therapeutically equivalent product in place of the one named on the prescription, unless the prescriber has excluded substitution by crossing out the aut-idem field.
The term comes from the words physicians once wrote on a prescription. Adding aut idem, "or the same", next to a product authorised the pharmacy to hand out an equivalent instead. German prescription practice then inverted the phrase into a control box: substitution is now the default, and the physician switches it off, not on. The purpose stated by the legislator is economic. The obligation to dispense a lower-priced, wirkstoffgleiches alternative is meant to reduce medicine expenditure in the statutory health insurance system, which is why aut idem and the Rabattvertrag work as one mechanism rather than two.
On the standard prescription form the aut-idem field is a box the physician crosses to forbid substitution. Crossed means the exact product prescribed must be dispensed. Left blank, or where the doctor prescribed only by active ingredient, the pharmacy is obliged to substitute under §129 Abs. 1 SGB V. The logic is counterintuitive and worth stating plainly: an unmarked box permits the exchange, a marked box blocks it.
§129 Abs. 1 Satz 2 SGB V defines the substitutability test. A product may replace the prescribed one only if all of the following hold.
The everyday shorthand calls these the four aut-idem criteria: active ingredient, strength, dosage form and indication. The statute adds identical pack size as a hard requirement, which is why an N2 pack cannot substitute for an N3. The dosage-form criterion carries most of the practical difficulty, because two forms can be therapeutically comparable without being identical. A hard capsule and a film-coated tablet, for example, may or may not count as interchangeable depending on the release characteristics. That is exactly why the statute delegates the judgement to the G-BA, whose Teil A list of interchangeable dosage forms removes the guesswork at the counter and gives the pharmacy a binding reference.
Some medicines are excluded from substitution regardless of the aut-idem box. Under §129 Abs. 1a SGB V the G-BA determines the medicines for which substitution by a wirkstoffgleiches Arzneimittel is excluded, focusing above all on substances with a narrow therapeutic index (geringe therapeutische Breite). These are listed in Teil B of Anlage VII (Abschnitt M) of the AM-RL, known in practice as the Substitutionsausschlussliste. A product on that list is dispensed exactly as prescribed, even when the box is blank and a rebate contract exists. The G-BA sets three cumulative criteria for adding a substance: a minor change in dose or plasma concentration already produces clinically relevant effects, substitution can cause clinically relevant impairment beyond individual cases, and the Fachinformation requires therapy monitoring that a swap could not proceed without.
Substitutability is the gate; the Rabattvertrag decides which product goes through it. Once a product is substitutable and not excluded, §129 Abs. 1 SGB V directs the pharmacy to prioritise a product covered by a §130a Abs. 8 agreement (Rabattvertrag) with effect for the patient's fund. Aut idem answers "may I swap", and the rebate contract answers "swap to which". If no rebate contract applies, the pharmacy substitutes toward a lower-priced product under the framework contract. The Rabattvertrag entry sets out that priority in full.
These two are routinely confused, and the difference is substantive.
| Aut idem | Aut simile | |
|---|---|---|
| Literal meaning | "Or the same" | "Or something similar" |
| What changes | The manufacturer only; same active ingredient, strength and interchangeable dosage form | The substance itself; a different but comparable active ingredient or formulation |
| Legal basis | Substitution obligation under §129 Abs. 1 SGB V | Not covered by the §129 substitution obligation |
| Who decides | The pharmacy, unless the prescriber excluded it | Generally requires the prescriber's agreement, because the substance changes |
In short, aut idem stays on the same active ingredient and swaps the maker. Aut simile moves to a merely comparable product and is not what the statutory substitution rule permits.
The comparison and substitution fields sit in the Vergleichssuche block of the article detail page, drawn from the licensed ABDA article master data.
One honest limitation: these fields help you narrow the candidate set, but the binding aut-idem decision always rests on the current §129 SGB V criteria, the G-BA Substitutionsausschlussliste and the fund-specific Rabattvertrag, all of which change over time. A stored comparison field is only as current as its last update, so treat it as a research aid, not as the legal ruling.
