In most cases, it is safe to take two tablets of a lower dosage to equal a new, higher dose of the same drug you have been prescribed.
This holds true, even if your drug products are extended-release formulation; those which have a coating or mechanism to release the drug slowly.
One example of an extended release drug that is available in multiple strengths is Effexor XR. It is available in the following strengths:
- Effexor XR 37.5 mg
- Effexor XR 75 mg
- Effexor XR 150 mg
- Effexor XR 225 mg
In the case of Effexor XR, if you were initially prescribed 37.5mg and were raised to 75mg, it would be safe for you to take two 37.5mg capsules to equal your new dose until you can get a prescription for the Effexor XR 75mg. This ensures your previous prescription doesn't go to waste.
There are a few exceptions to simply taking two doses of your lower strength product however. One is with the drug Nucynta ER. While you can take more than one tablet, it is important that only one tablet be taken at a time. Each tablet should be taken with enough water to ensure complete swallowing immediately after taking by mouth.
As you didn't specify the drug in your question, we can't give pointed advice. Be sure to talk to your doctor or pharmacist about your specific product.