Will pseudoephedrine hydrochloride affect a drug test?

Possibly. "false positive testing" occurs when a test finds evidence of illegal drug use when no drugs were taken. This can be a result of some over-the counter medications having chemical structures similar to illegal drugs. Pseudofed, found in many allergy and "cold" medications is one of these drugs.
It can. If it is a screening test, sudafed will often result in a positive amphetamine test. However, screening tests should be confirmed by more sophisticated testing, which will tell the difference between amphetamine and sudafed. If they are just doing a dipstick urine test (schools, employers etc often just do this), you may get into trouble for a false positive test.

Related Questions

Should I be careful with a drug with the following active agents:paracetamol 500mg/pseudoephedrine hydrochloride 60mg/triprolodine hydrochloride2.5mg?

It's not candy. It is a combo pill of Acetaminophen (liver toxc in high doses, > 3000 -4000mg/d), decongestant/stimulant (can cause rapid heartrate, increased bp, anxiety, palpitations, insomnia) and an antihistamine (dry you out, drowsy). Typically available without prescription. Cautions with heart, thyroid, bp, prostate, anxiety, other conditions. Don't overdo, take alcohol, ; careful w/other meds. Check w/md. Read more...
Follow doc's instrxn. Taking the med as directed either by doc or on package label should keep u safe. Paracetamol = tylenol (acetaminophen) (so don't take extra tylenol (acetaminophen)); Pseudoephedrine is decongestant (shrinks membranes, reduces congestion; may elevate blood pressure); triprolidine is antihistamine that can cause sedation; so no alcohol when taking this med. Read more...