" Bath salts " (also called "psychoactive bath salts" or "PABS" )   is a term used in North America and Europe to describe a number of recreational designer drugs.   The name derives from instances in which the drugs were sold disguised as true bath salts.    The white powder, granules, or crystals often resemble true bath salts such as Epsom salts, but are very different chemically. The drug's packaging often states "not for human consumption" in an attempt to circumvent drug prohibition laws.  Bath salts have also been similarly disguised as plant food, hookah cleaner, and other products.
Synthetic cathinones such as mephedrone, which are chemically similar to cathinone, naturally found in the plant Catha edulis (khat), were first synthesised in the 1920s.  They remained obscure until the first decade of the 21st century, when underground chemists rediscovered them and began to use them in designer drugs, as the compounds were legal in many jurisdictions.  In 2009 and 2010 there was a significant rise in the abuse of synthetic cathinones, initially in the United Kingdom and the rest of Europe, and subsequently in the United States. Drugs marketed as "bath salts" first came to the attention of authorities in the US in 2010 after reports were made to US poison centers.  In Europe, the drugs were predominantly purchased from websites, but in the US they were mainly sold in small independent stores such as gas stations and head shops.  In the US, this often made them easier to obtain than cigarettes and alcohol.  Bath salts have also been sold online in small packets. 
Hundreds of other designer drugs or "legal highs" have been reported, including artificial chemicals such as synthetic cannabis and semi-synthetic substances such as methylhexaneamine.  These drugs are primarily developed to avoid being controlled by laws against illegal drugs, thus giving them the label of designer drugs. 
In the US, the number of calls to poison centers concerning "bath salts" rose from 304 in 2010 to 6,138 in 2011, according to the American Association of Poison Control Centers.  Calls related to bath salts then began to decrease; by 2015, the number had declined to 522. 
Pharmacologically, bath salts usually contain a cathinone, typically methylenedioxypyrovalerone (MDPV), methylone or mephedrone ; however, the chemical composition varies widely   and products labeled with the same name may also contain derivatives of pyrovalerone or pipradrol. In Europe the main synthetic cathinone is mephedrone, whereas in the US MDPV is more common. 
Very little is known about how bath salts interact with the brain and how they are metabolised by the body. Scientists are inclined to believe that bath salts have a powerful addictive potential and can increase users' tolerance.   They are similar to amphetamines in that they cause stimulant effects by increasing the concentration of monoamines such as dopamine, serotonin, and norepinephrine in synapses.   They are generally less able to cross the blood brain barrier than amphetamines due to the presence of a beta-keto group that increases the compound's polarity. 
Bath salts can be ingested, snorted, smoked, or injected. Injection is especially ill-advised as these products rarely list ingredients, let alone dosage. Bath salts are known to be detrimental to human health and have been known to cause erratic behaviour, hallucinations and delusions.
Users of bath salts have reported experiencing symptoms including headache, heart palpitations, nausea, and cold fingers. Hallucinations, paranoia, and panic attacks have also been reported,  and news media have reported associations with violent behavior,  heart attack, kidney failure, liver failure, suicide, an increased tolerance for pain,  dehydration, and breakdown of skeletal muscle tissue. 
Interaction with alcohol
Bath salts are very often consumed concurrently with alcohol. A 2015 study  has investigated the interrelation between mephedrone and alcohol, focusing on psychostimulant and rewarding effects. It showed that alcohol, at low (non-stimulant) doses, significantly enhances the psychostimulant effects of mephedrone. This effect is mediated by an increase in synaptic dopamine, as haloperidol, but not ketanserin, was capable of blocking the potentiation by alcohol.
MDPV cannot be smelled by detection dogs  and will not be found in typical urinalysis,  although they can be detected in urine and hair analyses using gas chromatography-mass spectrometry.   Distributors may disguise the drug as everyday substances such as fertilizer or insect repellent.  
Little is known about how many people use bath salts.  In the UK, mephedrone, commonly known as MCAT, is the fourth most commonly used drug among nightclub goers after cannabis, MDMA and cocaine.  Based on reports to the American Association of Poison Control Centers, use of bath salts in the US is thought to have increased significantly between 2010 and 2011.  The increase in use is thought to result from their widespread availability, undetectability on many drug tests, and sensationalist media coverage. 
Users tend to range from ages 15–55 with the average being age 28. 
The drug policy of Canada is that during the fall of 2012, methylenedioxypyrovalerone (MDPV) will be categorised as a schedule I substance under the Controlled Drugs and Substances Act, placing it in the same category as heroin and MDMA.  Mephedrone and methylone are already illegal in Canada and most of the United States. 
In the United Kingdom, all substituted cathinones were made illegal in April 2010,   under the Misuse of Drugs Act 1971, but other designer drugs such as naphyrone appeared soon after  and some products described as legal contained illegal compounds.  To avoid being controlled by the Medicines Act, designer drugs such as mephedrone have been described as "bath salts", or other misnomers such as "plant food" despite the compounds having no history of being used for these purposes.   
In July 2012, US federal drug policy was amended to ban bath salts.  Prior to that, bath salts were illegal in at least 41 states.  Prior to the compounds being made illegal, mephedrone, methylone, and MDPV were marketed as bath salts.  The "bath salt" name and labels that say "not for human consumption" are an attempt to skirt the Federal Analog Act, which forbids selling drugs that are substantially similar to drugs already classified for human use.