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:
Did the drug my doctor prescribed me cause my hair loss?
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 on this reaction?
Yes (+1) No (0) Do not know or not done (0)
2. Did the adverse events appear after the suspected drug was given?
Yes (+2) No (-1) Do not know or not done (0)
3. Did the adverse reaction improve when the drug was discontinued or a specific antagonist was given?
Yes (+1) No (0) Do not know or not done (0)
4. Did the adverse reaction appear when the drug was readministered?
Yes (+2) No (-1) Do not know or not done (0)
5. Are there alternative causes that could have caused the reaction?
Yes (-1) No (+2) Do not know or not done (0)
6. Did the reaction reappear when a placebo was given?
Yes (-1) No (+1) Do not know or not done (0)
7. Was the drug detected in any body fluid in toxic concentrations?
Yes (+1) No (0) Do not know or not done (0)
8. Was the reaction more severe when the dose was increased, or less severe when the dose was decreased?
Yes (+1) No (0) Do not know or not done (0)
9. Did the patient have a similar reaction to the same or similar drugs in any previous exposure?
Yes (+1) No (0) Do not know or not done (0)
10. Was the adverse event confirmed by any objective evidence?
Yes (+1) No (0) Do not know or not done (0)
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 https://www.evidencio.com/models/show/661 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.
This article was written by Dr. Jeff Donovan, a Canadian and US board certified dermatologist specializing exclusively in hair loss.