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Lethal dose (LD50) testing

FRAME believes that the lethal dose test (known as LD50) is unnecessarily cruel and scientifically invalid. The test involves giving groups of animals doses of a test substance until it kills half of them.


There are three valid alternative methods for testing acute oral toxicity of chemicals and FRAME believes they should be used to avoid the suffering involved in LD50.

Additional information

The classical LD50 test for oral toxicity is no longer recognised by the OECD (Organisation for Economic Co-operation and Development), the international governments’ advisory body. However, it remains the responsibility of individual countries to change their laws. Regulatory authorities worldwide require all chemicals to undergo acute oral toxicity tests. Requirements vary, but most stipulate testing in two rodent species.


The deletion of the LD50 test from the OECD guidelines was due to three alternative methods being adopted which all involve more humane treatment of the animals involved and also use far fewer animals than the LD50 test. FRAME recommends the FDP method because it is the most humane.

These three tests are:

Fixed Dose Procedure (FDP) — OECD TG 420. This method does not use death as an endpoint, instead it uses the observation of clear signs of toxicity developed at one of a series of fixed dose levels to estimate the LD50.

Acute Toxic Class method (ATC) — OECD TG 423. This method does not use death as the only endpoint, it also uses signs of toxicity in its stepwise approach to estimating the LD50.

Up-and-Down Procedure (UDP) — OECD TG 425. This method does still use death as an endpoint, but doses animals one at a time to see if the dose needs to be put up or down to achieve an estimate of the LD50 therefore giving the minimum number of animals a lethal dose of the test substance.