2,4-Dinitrophenol (2,4-DNP or simply DNP) is an organic compound with the formula . It occurs as yellow crystals or platelets. It has been used in explosives manufacturing and as a pesticide and herbicide.

In humans, DNP causes dose-dependent mitochondrial uncoupling, causing the rapid loss of ATP as heat and leading to uncontrolled hyperthermia—up to —and death in case of overdose. Researchers noticed its effect on raising the basal metabolic rate in accidental exposure and developed it as one of the first weight loss drugs in the early twentieth century. DNP was banned from human use by the end of the 1930s due to its risk of death and toxic side effects. DNP continues to be used after its ban and experienced a resurgence in popularity after it became available on the Internet.

Chemical properties

<!-- thumb|upright=0.6|Chemical structure of DNP -->

thumb|upright=1.3|Synthesis of DNP (right) from [[phenol and nitric acid via 2-Nitrophenol and 4-Nitrophenol]]

It sublimes, is volatile with steam, and is soluble in most organic solvents as well as aqueous alkaline solutions. Nitration of phenol is not practical commercially because partial decomposition of the phenolic ring occurs. DNP forms explosive salts with strong bases as well as ammonia, and emits toxic fumes of nitrogen dioxide when heated to decomposition.

Uses

Industrial

Historically, DNP has been used as an antiseptic and as a non-selective bioaccumulating pesticide.

DNP was particularly useful as a herbicide alongside other closely related dinitrophenol herbicides like 2,4-dinitro-o-cresol (DNOC), dinoseb and dinoterb. Since 1998 DNP has been withdrawn from agricultural use. Currently, there are no actively registered pesticides containing DNP in the United States or Europe.

It is a chemical intermediate in the production of sulfur dyes, wood preservatives A precursor to 2,4,6-trinitrotoluene (TNT), DNP has also been used to make photographic developers and explosives.

In humans

thumb|upright=0.9|[[Histogram of DNP doses reported on online forums and the subreddit /r/DNP Although DNP is no longer in clinical use as a weight loss drug due to its dangerous side effects, its mechanism of action remains under investigation as a potential approach for treating obesity and non-alcoholic fatty liver disease.

DNP is used by bodybuilders, fitness enthusiasts, and people with an eating disorder to lose weight. The user profile is similar to that of anabolic steroids; many perceive it to be effective and with manageable risks. Despite health warnings from regulators, DNP is readily available online sometimes under other names such as Dinosan, Dnoc, Solfo Black, Nitrophen, Aldifen, and Chemox. According to a study published in 2023, the most commonly reported doses were between . Between 2010 and 2020, reports of overdoses were higher in Australasia, Europe and North America than in Asia, Africa, and South or Central America.

Pharmacokinetics

Information about pharmacokinetics and pharmacodynamics of DNP in humans is limited. DNP is metabolized via nitro reduction. Its major metabolites are 2-Amino-4-nitrophenol and 4-amino-2-nitrophenol. In overdoses, symptom onset can be as soon as 3 hours and the average time to death was 14 hours. Contact with skin or inhalation can cause DNP poisoning. Symptoms are typically mild with dermal exposure, but inhalation can lead to systemic effects, the same way as oral exposure. Although the lowest published fatal ingested dose is , a typical overdose death occurs at a higher level of exposure, around .

The first symptoms to appear are nausea, vomiting, abdominal pain, and perhaps diarrhea. The typical overdose syndrome seen with DNP and other phenols is a combination of hyperthermia, tachycardia, diaphoresis, and tachypnoea. Because of the heat produced during uncoupling, DNP overdose will overpower the body's attempt to maintain thermal homeostasis and cause an uncontrolled, fatal rise in body temperature up to as high as . The disruption of metabolism also leads to the accumulation of potassium and phosphate, potentially contributing to toxicity. DNP can cause T wave and ST segment abnormalities; heart muscle, kidney, and liver damage have been found on autopsy.

There is no antidote to DNP and management strategies are based on expert opinion and case studies. Treatment for overdose is supportive, and often involves aggressive cooling using methods such as ice baths and intravenous fluids.

DNP's risks were highlighted in the Chamber of Horrors, an exhibit assembled by the United States Food and Drug Administration (FDA) to explain the limitations of existing American drug regulations. In 1938, the Food, Drug, and Cosmetic Act increased the FDA's ability to regulate drugs. DNP was deemed so toxic as to be banned for human consumption and in 1940 the FDA reported that there was no evidence of continued sale for this purpose.

As a pollutant

Although many militaries are replacing traditional 2,4,6-trinitrotoluene (TNT)-based explosives for insensitive munitions, DNP is a degradation byproduct of the IMX-101 insensitive munition used by the United States Army.

While the Meisenheimer charge transfer reaction is effective at detecting TNT, it is not effective at detecting many other explosives including DNP. Researchers are studying colorimetric detection and other methods for DNP to find if water or solids such as soils are contaminated with DNP. UiO-66-NH<sub>2</sub> can be used to bind to and remove DNP from solution.

DNP is banned for human consumption in many countries. DNP has been banned by the World Anti-Doping Association since 2015.

Petróczi et al. recommend against campaigns informing people of the risks of DNP because it could increase use of the drug. In 2018, a seller in the United Kingdom was convicted of manslaughter for selling DNP for human consumption. The conviction was sent to retrial in 2020 by the English Court of Appeal, where the seller was, once again, convicted of gross negligence manslaughter.

The UK government reclassified DNP as a regulated poison with effect from October 2023.

References

  • Athlete dies at the 2025 Arnold Classic