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Substance abuse and dependence are steadily increasing problems in the United States. This is extremely serious, because many of these substances of abuse are prescription medications.

Although most doctors are aware of the most commonly abused prescription medications, such as benzodiazepines and narcotics, centrally acting skeletal muscle relaxants are also being abused, even though this is not as widely recognized fact. About 1% of American adults are taking muscle relaxants, often on a chronic basis. Some of these users are taking muscle relaxants because they have all the proper indications, but a vast majority of them have developed a habit. Where is the line between actual need and abuse?

Biochemical structure and mechanism of action of muscle relaxants

Biochemically, skeletal muscle relaxants are a diverse group of drugs. Some of them belong to the group of tricyclic antidepressants such as Cyclobenzaprine (Flexeril® ); some of them are derivates of gamma-aminobutyric acid such as Baclofen (Lioresal® ), and some of them are similar chemical structure to other medications like with carisoprodol (Soma® ), which is in turn chemically related to meprobamate (Equanil® , Miltown® ).

The mechanism of action of skeletal muscle relaxants is largely unknown. However, certain animal studies have suggested that they depress polysynaptic reflexes. Because of their various chemical structures, there could cause some serious problems.

Besides all these properties, almost all muscle relaxants posses some kind of sedative property, which is why they are being abused in the first place. Recent studies have confirmed that, when taken in high doses, they cause a buzz, sense of euphoria. and mood enhancement, as well as pleasant misperceptions.

Drugs classified as skeletal muscle relaxants include:

  • cyclobenzaprine (Flexeril® )
  • dantrolene (Dantrium® )
  • metaxalone (Skelaxin® )
  • baclofen (Lioresal® )
  • carisoprodol (Soma® )
  • chlorzoxazone (Paraflex® )
  • methocarbamol (Robaxin® )
  • orphenadrine (Norflex® )
  • tizanidine (Zanaflex® )

History of muscle relaxant abuse

Muscle relaxants were not a subject of abuse debates until a few years back, when they have taken center stage after several reports of deaths due to abuse of such a drug. That’s when some medication approval agencies started to recognize the problem.

Only a few years later, in 1996 and 1997, several members of hospital staff were charged for murdering six elderly hospital patients by overdose of two muscle relaxants - Pavulon and succinylcholine chloride (SUCC), commonly abused medications today. According to the medical charts of these patients, they choked to death when medications started to shut down their respiratory systems.

Another incident occurred with a medication called Raplon®, which was a very popular muscle relaxant until the report of five deaths related to it. Although useful, Raplon® was pulled from the market because it interferes with normal breathing.

To understand the danger of muscle relaxants, we should point out that Raplon® was the twelfth drug removed from the market since 1997. Before that, the FDA didn’t pull these medications from the market although many people were questioning the rapid approval of drugs.

Indications for muscle relaxant use

The main indications are two different types of underlying conditions:

Spasticity from upper motor neuron syndromes: The term spasticity indicates a specific clinical condition characterized by a velocity-dependent increase in tonic stretch reflexes or muscle tone. This condition is often associated with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex. There are several conditions specifically associated with spasticity, such as multiple sclerosis, spinal cord injury, traumatic brain injury, and cerebral palsy.

Muscular pain or spasms from peripheral musculoskeletal conditions: Muscle spasm is defined as a sudden involuntary contraction of one or more muscle groups. It usually represents an acute condition associated with muscle strain or sprain. The most common symptoms are tenderness and muscle spasms, fibromyalgia, tension headaches, myofascial pain and low back or neck pain.

When used in these situations, to treat these conditions, muscle relaxants can be extremely useful. They relax certain muscles in the body and relieve the stiffness, pain and discomfort caused by strains, sprains, or other injury.

The FDA has approved only a few medications in this class for treatment of spasticity. All others are prohibited or still under the investigation of FDA.

Muscle relaxants abuse facts

Muscle relaxants are rarely taken alone. In most cases they are used in combination with other central nervous system depressants, such as alcohol, benzodiazepines, or narcotics. The relaxants prolong the effect of alcohol or a narcotic, or even increase it. Additionally, prescriptions for skeletal muscle relaxants are usually easier to obtain than prescriptions for narcotics. They are also less expensive.

Sometimes addicts take muscle relaxants to demonstrate signs of tolerance, and also suffer withdrawal symptoms of anxiety, tremors, insomnia and, occasionally, hallucinations or seizures.

Side Effects and Adverse reactions

All skeletal muscle relaxants may cause sedation (drowsiness, dizziness). This is almost a rule for them. There are also other effects characteristic to some of them individually; for example, Baclofen may cause severe central nervous system depression with cardiovascular collapse and respiratory failure, while Dantrolene has a potential for hepatotoxicity. Carisoprodol, like many other muscle relaxants, has some potential for dependence and withdrawal symptoms. Several patients, after using Methocarbamol and chlorzoxazone, have noticed that their urine has changed color into something like orange or reddish-purple. This is reported by many patients later and classified as a harmless side effect, as the urine will return to its normal color when the patient stops taking the medicine.

The conclusion 

Because of the fact that the relaxants act on the central nervous system, their actions may produce some side effects associated with CNS functioning. That’s why in most countries they are strictly prohibited, while in others, some can be sold even without prescription. Although they were once sold and used widely with no control of medication agencies because no side effects were reported, today the situation has changed. Because of so many reported abuses and deaths using muscle relaxants, patients and governments agencies have become cautious. However, these are still extremely useful medications for muscle relaxation in clinical practice.

Like all other medications, they can cause several possible side effects, which is why they should be used with extreme caution. Countries where muscle relaxants can be bought easily, even without a doctor’s prescription, should change their pharmacy laws and prohibit this in the future.