The former Will & Grace star is a paid spokesperson for the drug and admits it's the only thing that has helped her combat a myriad of allergies.

She tells Access Hollywood Live, "Before I discovered Zyrtec I was on several different projects where we had to shut down because I had a horrible allergy attack.

"One of them was (film) The Wedding Date... We were shooting outside in the beautiful English countryside and my throat just started to close and my face turned red and I was tearing (up) and everything got puffy.

"The director came in and was like, 'What's up?' and I'm like, 'I'm having an allergy attack and they said, 'OK everybody, take a break', and we waited, like, four hours."

Last year (14), when she signed on to endorse Zyrtec, she called the drug "a revelation", adding, "I found something that I could take in the morning and I was set for 24 hours and I could go out in the park and play soccer with my son and not worry about it.

"I could shoot... out in Central Park after the rain and not worry about my eyes turning bright red and sounding like (throaty actress) Brenda Vaccaro because of having an allergic reaction."

The medication has also solved Messing's snoring problem.