Analgesics are medications that prevent the body from feeling pain. They work by either stopping pain signals from reaching the brain or altering the brain’s interpretation of those signals. Although analgesics block pain, they do not treat the underlying condition that is responsible for the pain.

They are used to treat pain related to many conditions, including:

• Arthritis and other types of joint pain
• Headaches
• Back pain, including herniated discs, degenerative disc disease and spinal stenosis

• Whiplash, burns and other types of trauma pain
• Chest pain, abdominal pain and pelvic pain
• Labor and surgical pain
• Orofacial pain and dental pain
• Chronic pain disorders such as fibromyalgia, chronic fatigue syndrome and lupus
• Sickle cell anemia crises
• Cancer pain 

Narrowly defined, analgesics include opioids such as codeine and non-narcotic painkillers such as acetaminophen. However, many other classes of drugs are also used to relieve pain. Among these are anti-inflammatories, which include corticosteroids such as hydrocortisone, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, naproxen and COX-2 inhibitors.

Some medications that primarily treat other conditions are also used to reduce pain. For example, antidepressants treat many pain conditions, lithium can be prescribed as a preventive headache medication, anticonvulsants (seizure medications) relieve conditions ranging from cranial neuralgias to restless leg syndrome to diabetic neuropathy, antihistamines can treat conditions including headaches and chest pain, anti-malarial and chemotherapy drugs sometimes ease lupus, and antihypertensives (blood pressure drugs) can be prescribed for headaches, chest pain or benign prostatic hyperplasia.

Other classes of drugs that can be used to relieve pain conditions include muscle relaxants, immunosuppressives such as DMARDs and biologic response modifiers, psychostimulants, marijuana-like cannabinoids, nerve blocks and other anesthetics used in injection therapy, antibiotics and other antimicrobials for conditions ranging from Lyme disease to Reiter’s syndrome, and digestive-tract medications such as antispasmodics and proton pump inhibitors for abdominal and chest pain.

Substances being studied for use in pain relief include the wrinkle treatment botulinum toxin A (Botox), which studies have shown to be promising against conditions including migraines, orofacial pain and tennis elbow; supplements such as glucosamine and chondroitin; and sugar, which has been found to reduce pain in children.

Analgesics can be administered in several ways, including:

• Oral. Delivered in liquid or pill form.
  
  
• Creams, gels or ointments. Topical analgesics applied over painful areas.
  
  
• Skin patch. A bandage-like patch that gradually and continuously releases medicine through the skin over two or three days.
  
  
• Suppository. Medicine that dissolves in the rectum and is absorbed into the body.
  
  
• Intravenous. Injection into a vein.
  
  
• Subcutaneous. Needle placed just under the skin.
  
  
• • Continuous infusion. The slow introduction of a fluid into a blood vessel, usually over a prolonged period of time.
    
    
  • Pump. Known as patient-controlled analgesia (PCA), a pump allows a patient to push a button that delivers a preset dose of medication.
    
    
• Intrathecal. Needle placed into fluid around the spinal cord.
  
  
• Epidural. Needle placed into space around the spinal cord.

Patients who have chronic pain will usually receive long-acting analgesics regularly according to a schedule called "around the clock" (ATC). This is often done even if it requires waking the patient and is usually done with longer acting narcotic painkillers. Patients should not experience any pain before the next dosage is administered and should consult their physician if treatment is not controlling their pain.