• results vary between species
• results vary between the same species
• even identical animals in identical surroundings give varying results

Due to:

• temperament of the animal
• temperature in the laboratory
• cage design (grid or flat surface)
• state of the weather
• the season of the year
• sex, age and disposition of the animal
• type of food (starved or fed) (many animals are starved before being administered the substance)
• type of bedding
• body weight of the animal
• humidity

All these factors and many more make it impossible to standardise animals - they simply will not be made into inanimate objects but each one insists on being a living being in its own right.

At this point it may be appropriate to give just a few of the countless known examples of species differences.

• The heart drug practolol caused blindness in many patients but this effect has never been reproduced in animals.
• Morphine sedates man, rats and dogs but has entirely the opposite effect on cats, goats and horses.

While animal tests can give a misleading impression of safety - by the same token they can also result in the discarding valuable drugs. If penicillin had been tested on guinea-pigs or hamsters during its development we probably wouldn't have this antibiotic today. Many useful drugs have been introduced into medicine without previous animal tests: for instance the earliest inhalation anaesthetics, digitalis and cinchona bark, which is a natural source of quinine and an early treatment for malaria. As Koppanyi and Avery have explained:

"Had they first been tested on animals some might never have reached clinical trials."

Opren and Oraflex... The former the United Kingdom name and the latter the United States name for the same anti-arthritis drug Benoxaprofen was removed from the market recently after killing at least 61 people. For seven years this drug was relentlessly tested on animals.

Proving over and over again that undue emphasis is being placed on dubious and unreliable tests involving animals - and the utter futility of trying to determine the merits of drugs designed to alleviate the ills of humanity by methods which, being wholly inadequate may well produce data that is dangerous and misleading when applied to humans.