Did my drug cause hair loss?

The Naranjo Adverse Drug Reaction Probability Scale

Anything applied to the skin or taken by mouth has the potential to cause a side effect. Some medications rarely cause side effects and others tend to cause frequent side effects. Occasionally a patient will report a side effect that perhaps has never been reported before. The question then becomes - is this a real side effect from the drug or is it happening from something else?

In my clinic, the cause and effect relationship of a drug and a side effect become relevant in a wide range of situations. Common examples include:

  1. Did the drug my doctor prescribed me cause my hair loss?
  2. Did the drug given for my hair loss cause me to develop this side effect I am worried about (fatigue, muscle pain, leg twitching, abnormal blood tests)?


A Closer Look at the Naranjo Adverse Drug Probability Scale

The Naranjo Scale was created nearly 40 years ago to help standardize how clinicians to about assessing whether or not a drug could be implicated in an adverse drug reaction. It is used in controlled clinical trials. The scale is quite easy to use - and involves asking the patient 10 questions. Answers to the question are recorded as "yes", "no" or "don't know" and different points are assigned to each answer (-1, 0, +1, +2). 

Typical Questions in the Naranjo Scale

  1. Are there previous conclusive reports of this reaction? 
  2. Did the adverse event appear after the drug was given?
  3. Did the adverse reaction improve when the drug was discontinued or a specific antagonist was given?
  4. Did the adverse reaction reappear upon readministering the drug?
  5. Were there other possible causes for the reaction?
  6. Did the adverse reaction reappear upon administration of placebo?
  7. Was the drug detected in the blood or other fluids in toxic concentrations?
  8. Was the reaction worsened upon increasing the dose? Or, was the reaction lessened upon decreasing the dose?
  9. Did the patient have a similar reaction to the drug or a related agent in the past?
  10. Was the adverse event confirmed by any other objective evidence?
  12. Determining the Naranjo Score

Scores can range from -4 to + 13. A score of 0 or less means the likelihood of the drug causing the side effect is doubtful, a score 1 to 4 indicates it is 'possible', a score 5 to 8 means it is 'probable' and a score 9 to 13 means it is 'definite'


Calculating the Naranjo Score

The website http://www.pmidcalc.org/index.php provides a free online calculator for clinicians to calculate the Naranjo Score. It is easy to use and has been embedded below as an example. Individuals wanting to know if a specific drug caused hair loss should be sure to speak to their dermatologist. 



Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Whistler office at 604.283.1887

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