Thujone is a ketone and a monoterpene that occurs naturally in two diastereomeric forms: (-)-α-thujone and (+)-β-thujone. It has a menthol odor. Though it is best known as a chemical compound in the spirit absinthe, absinthe contains only small quantities of thujone, so thujone is unlikely to be responsible for absinthe's alleged psychedelic effects. Thujone acts on GABA and 5-HT₃ receptors in the brain. In many countries, the amount of thujone allowed in food or drink products is regulated. Thujone, as a component of several essential oils, is also used in perfumery.

In addition to the naturally occurring (-)-α-thujone and (+)-β-thujone, two other enantiomeric forms are possible: (+)-α-thujone and (-)-β-thujone.

Thujone is found in a number of plants, such as arborvitae (genus Thuja, hence the derivation of the name), Nootka cypress, some junipers, mugwort, oregano, common sage, tansy, and wormwood, most notably grand wormwood (Artemisia absinthium), usually as a mix of isomers in a 1:2 ratio. It is also found in various species of Mentha (mint).

People use camphor topically to relieve pain and reduce itching. It has also been used to treat fungal infections of the toenail, warts, cold sores, hemorrhoids, and osteoarthritis.

Camphor is used topically to increase local blood flow and as a “counter irritant,” which reduces pain and swelling by causing irritation. It is important not to apply camphor to broken skin, because it can enter the body quickly and reach concentrations that are high enough to cause poisoning.

Some people use camphor topically to treat respiratory tract diseases and to treat heart disease symptoms. Camphor is also used topically as an ear drop, and for treating minor burns.

Some people inhale camphor to reduce the urge to cough.

Although it is an UNSAFE practice, some people take camphor by mouth to help them cough up phlegm, for treating respiratory tract infections, and for intestinal gas (flatulence). Experts warn against doing this because, when ingested, camphor can cause serious side effects, even death.

Camphor is a well-established folk remedy, and is commonly used. Camphorated oil (20% camphor in cottonseed oil) was removed from the U.S. market in the 1980s because of safety concerns. It continues to be available without a prescription in Canada.

Citral is a clear yellow colored liquid with a lemon-like odor. Less dense than water and insoluble in water. Toxic by ingestion. Used to make other chemicals.

Citral is present in the oils of several plants, including lemon myrtle, Litsea citrata, Litsea cubeba, lemongrass, lemon tea-tree, Ocimum gratissimum, Lindera citriodora, Calypranthes parriculata, petitgrain, lemon verbena, lemon ironbark, lemon balm, lime, lemon, and orange.

Geranial has a strong lemon odor. Neral's lemon odor is less intense, but sweeter. Citral is therefore an aroma compound used in perfumery for its citrus effect. Citral is also used as a flavor and for fortifying lemon oil. It also has strong antimicrobial qualities, and pheromonal effects in insects.

Pulegone is a naturally occurring organic compound obtained from the essential oils of a variety of plants such as Nepeta cataria (catnip), Mentha piperita, and pennyroyal. It is classified as a monoterpene. Pulegone is a clear colorless oily liquid and has a pleasant odor similar to pennyroyal, peppermint and camphor. It is used in flavoring agents, in perfumery, and in aromatherapy.