Along with its needed effects, clindamycin may cause some unwanted or undesirable effects. Generally, clindamycin is well tolerated and many people will not experience unwanted effects. The frequency and severity of these effects is dependant on many factors including dose, duration of therapy and individual susceptibility. Possible unwanted effects include:
Common:

• diarrhea
• nausea
• rash

Uncommon:

• vomiting
• mouth sores
• sore throat
• bloody stools
• pseudomembranous colitis (inflammation of the colon caused by the overgrowth and toxin production of bacteria that are not killed by the antibiotic)

Clindamycin is an antibiotic medication that kills various bacteria. It works by inhibiting protein synthesis, resulting in bacterial cell death. The effectiveness of clindamycin depends on factors such as dose, concentration in the blood and other body fluids and tissues, and the susceptibility of the bacteria. Clindamycin does not kill all types of bacteria, but only those that have a sensitivity to this antibiotic. Infections caused by bacteria that are not sensitive to clindamycin will not show improvement after taking this medication.

Allergic reactions can occur with clindamycin use. The reaction can be immediate and severe. Allergic symptoms include wheezing, hives, itching, swelling, joint and muscle pain, difficulty breathing, fever and skin rashes. Nausea and vomiting are not symptoms of an allergic reaction.

Taking the antibiotic repeatedly or for prolonged periods may result in bacterial or fungal overgrowth which can lead to a second infection. When this occurs, the clindamycin may need to be stopped and another antibiotic prescribed to treat the new infection.
Diarrhea often develops while taking clindamycin. This is sometimes caused by an overgrowth of bacteria in the gut that are not killed by the antibiotic. In severe cases, this may be life threatening and would require treatment with other antibiotics. In mild cases, symptoms disappear shortly after the drug is discontinued.
Drug Interactions: It is important to tell your doctor and pharmacist of any prescription or over-the-counter medications you are taking. 

• BCG vaccine
• erythromycin
• mycophenolate
• primaquine
• sodium picosulfate
• typhoid vaccine

Use is not recommended in the following situations:

• allergy to clindamycin or lincomycin
• infants younger than 30 days

Caution is recommended in the following situations:

• diarrhea
• colitis or other digestive tract diseases
• liver disease

Use in pregnancy: Considered compatible with pregnancy.  Consult your doctor or pharmacist if you suspect you are pregnant.
Use while breastfeeding: Clindamycin does appear in breast-milk. Consult your doctor or pharmacist before use.