Trichloroethylene (or TCE), a synthetic chemical that does not occur naturally in the environment. TCE is used to make chemicals. Additionally, it is used for spot removal in dry cleaning operations. TCE is the most common organic contaminant in groundwater. It was revealed that the compound was a human carcinogen that caused liver cancer, kidney cancer, and non-Hodgkin's lymphoma (NHL).

Mephobarbital us a barbiturate derivative used primary as an anticonvulsant, but also as a sedative and anxiolytic. Marketing of mephobarbital was discontinued in 2012.

Aconitine is an alkaloid found in the Aconitum species. Aconitine is a highly toxic cardiotoxin and neurotoxin. In China and other countries, the herbal extract containing aconitine was used for the treatment of pain in musculoskeletal disorders, however the safety margin between therapeutic analgesic effect of aconitine and its known cardiotoxic effect is so narrow that the treatment may cause poisoning and death. The mechanism of aconitine action is explained by its ability to activate voltage-dependent sodium-ion channels.

QUININE HYPOPHOSPHITE, a salt of quinine, was formerly used, along with the hypophosphites of sodium, potassium, calcium, and iron, in the treatment of phthisis and neurasthenic conditions.

Theobromine is the primary alkaloid present in the cocoa and chocolate. Theobromine is found in the shells and beans of the cacao plant and it is extracted from the husks of the bean and used for the synthesis of caffeine. Theobromine is an adenosine A1 and A2a receptor antagonist. Thesodate is used as a vasodilator, a diuretic, and heart stimulant. And similar to caffeine, it may be useful in management of fatigue and orthostatic hypotension. The symptomatic adverse reactions produced by theobromine are more or less tolerable and if they become severe, they can be treated symptomatically, these include anxiety, restlessness, tremors, sleeplessness, nausea and vomiting, loss of appetite. Theobromine is currently not in use as a medicinal drug.

Melatonin (5-methoxy N-acetyltryptamine) is a hormone synthesized and released from the pineal gland at night, which acts on specific high affinity G-protein coupled receptors to regulate various aspects of physiology and behaviour, including circadian and seasonal responses, and some retinal, cardiovascular and immunological functions. Melatonin is also made synthetically and available without a prescription as an over-the-counter (OTC) dietary supplement in the U.S. Melatonin supplementation has many uses, however, it has been widely studied for treatment of jet lag and sleep disorders. Parents may consider using melatonin to help their child who has a trouble falling asleep. A medical professional should always evaluate insomnia or other sleeping disorders in children. Additionally, melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. In mammals, melatonin binds to a number of receptor subtypes including high-affinity (MT1 and MT2) and low-affinity (MT3, nuclear orphan receptors) binding sites, which are distributed throughout the central nervous system and periphery.

Aminophenazone is a phenyl-pyrazolone derivative with potent analgesic and antipyretic properties. Aminophenazone has been used as salt or complexes, including topically as the salicylate. It was recommended for the treatment of a fever, neuralgia, myositis, acute rheumatism, arthritis, chorea. In 1999 the FDA suspended aminophenazone. The drug caused agranulocytosis. Some of the cases of agranulocytosis were fatal. Another reason for suspending this drug from the market was its ability to react with nitrite-containing food, thus forming carcinogenic nitrosamines. A breath test with 13C-labeled aminopyrine has been used as a non-invasive measure of cytochrome P-450 metabolic activity in liver function tests.

Phenacetin was used as an analgesic and fever-reducing drug in both human and veterinary medicine for many years. Since a major portion of a dose of phenacetin is rapidly metabolised to paracetamol, it seems possible that phenacetin owes some of its therapeutic activity to its main metabolite, paracetamol, whereas its most troublesome side effect (methaemoglobinaemia) is due to another metabolite, p-phenetidine. Phenacetin was shown to inhibit cyclooxygenase (COX)-3, a cyclooxygenase-1 variant while p-phenetidine potently inhibits both COX-1 and COX-2. There is sufficient evidence in humans for the carcinogenicity of analgesic mixtures containing phenacetin. Analgesic mixtures containing phenacetin cause cancer of the renal pelvis, and of the ureter. Phenacetin was withdrawn from many analgesic mixtures long before the legal ban in several countries.

Acetanilide is a synthetic organic compound introduced clinically in 1886 as a fever-reducing drug. Its effectiveness in relieving pain was discovered soon thereafter and it was used as an alternative to aspirin for many years in treating such common complaints as headaches, menstrual cramps, and rheumatism. Unfortunately, Acetanilide exhibited an unacceptable profile of toxic effects, the most alarming being cyanosis due to methemoglobinemia. The toxic profile prompted the search for supposedly less toxic aniline derivatives such as phenacetin. After several conflicting results over the ensuing fifty years, it was established in 1948 that acetanilide was mostly metabolized to paracetamol (USAN: acetaminophen) in the human body and that it was the paracetamol that was responsible for the analgesic and antipyretic properties. Paracetamol has since replaced acetanilide usage because it is less likely to induce blood disorders. The observed methemoglobinemia after acetanilide administration was ascribed to the small proportion of acetanilide that is hydrolyzed to aniline in the body. Acetanilide is no longer used as a drug in its own right, although its primary metabolite, paracetamol, has been widely succesful.

Antipyrine is an analgesic and antipyretic that has been given by mouth and as ear drops. It is often used in testing the effects of other drugs or diseases on drug-metabolizing enzymes in the liver. It inhibits cyclooxygenases and shows little anti-inflammatory activity. Like many old and approved substances after almost 100 years of use, antipyrine has been associated with some serious side effects, namely agranulocytosis and shock reactions.