What expiration date means
We all need to keep some stock of modafinil at home or buy it when need to be concentrated. Nevertheless Modalert, Waklert, Artvigil, Modvigil and other modafinil / armodafinil brands are not cost that much, though sometimes remain unused before the expiration date. The temptation to use modafinil after the shelf life comes almost naturally. 
The date after which the manufacturers no more guarantee the proper effect and safety of a drug is called the expiration date. In India and many other countries drug producers are obliged to mark the expiration date on their products before selling. You will find this date on any modafinil brand or any other medicine marketed even without prescription and also on biologically active additives (BADs).
Average shelf-life
India FDA requires to estimate the expiration date of a drug through stability studies. Usually, pharmaceuticals marketed across the India have a shelf-life of 1-5 years. However, medicament producers typically test drug properties for up to 2-3 years – this shelf-life we see on most pharmaceuticals including modafinil amd armodafinil brands. 
Stability testing proves that some medicines could remain reliable for much longer, but no experiments were carried out. And, following liability and legal requirements, drug companies will not comment on using their expired production.
Also, once the original modafinil container is opened (by a patient or by a doctor dispensing the drug), the expiry date can no longer be trusted. There is no guarantee that ingredients, preservatives, light, temperature, humidity, and other storage conditions will not affect the stability of a drug after you open it. 
“Beyond use” dates
Concerning possible inadequate drug storage, U.S. Pharmacopeia (USP), an institution that determines medical quality standards, advises using “beyond use” dates. The obligatory in many State Boards of Pharmacy “discard after” or “best before” phrases followed by the date that is always earlier than the expiration one. 
Another pain is that annually we throw away expired medicals that have a considerable cost. According to Allen9, consumers, homes for the elderly, hospitals, and retail pharmacies write off unbelievable $800 million for pharmaceuticals each year.  
Shelf Life Extension Program (SLEP)
At the beginning of the 2000s, the American Medical Association (AMA) investigated that actual shelf-lives of some drugs are longer than those marked. FDA for the Department of Defense conducted the Shelf Life Extension Program (SLEP) that revealed the positive results. 
SLEP had two objectives: checking the actual expiration date of the stored military medicaments and decreasing state expenditures on medicals.  
One hundred and twenty-two pharmacies were reviewed in terms of the SLEP campaign. 88% of the drugs proved to be stable for 66 months (over five years) longer, and only 18% of these failed. Ciprofloxacin, morphine sulfate injection, amoxicillin, and diphenhydramine are the names of widely known medical products, which expiry date can be extended for 1 to over 15 years. However, the SLEP program did not cover biologics. 
Another factor that affects the shelf period of medicaments is package change: once placed in a different container, the drug storage life can decrease. The SLEP tested medicals in the original boxes.
Which drugs are more reliable after the expiry
It is not easy to say which medicine saves more properties after the expiration date due to insufficient information on this topic. However, solid drugs, such as pills and tablets, are the most stable against time. Suspensions or solutions, especially those be stored in the fridge (for example, amoxicillin suspension), do not keep their properties after the end date. 
A decrease in effectiveness is crucial for antibiotics that fight against infections. And, since such a drug may contain sub-potent medicaments, it is dangerous to use it after the expiration date. You should carefully examine solutions and injectables for any precipitants or even minor color change.
Drugs with preservatives (for example, ophthalmic eye drops) can be unsafe after the end date, as outdated preservatives let bacteria grow. 
Principles of using drugs
We can not know for sure unless the drug is tested, but some general principles applied to the expired medicaments might help. For example, insulin used to support the sugar level in the blood is sensitive to degradation. It is controversial among specialists, but tetracycline generates a metabolite, which is dangerous. Blood products, biologicals, and vaccines also quickly decompose upon expiry. When the bottle is opened, oral nitroglycerin (NTG) that treats angina may be spoiled fast.
If you take medicines that refer to heart diseases, cancer, dangerous allergy, or seizure, it would be better to get a new prescription beforehand. However, if you need a drug and cannot get a new one immediately, it is not proved that taking expired medicines is dangerous. But you need to keep in mind that expired drugs may not have the same therapeutic effect.
In case of minor health issues like moderate pain, headache, hayfever, sleepness or any similar conditions where modafinil (modalert, modvigil) and armodafinil (waklert, artvigil) comes into play it may be quite safe to get the expired medicament, though it may not help. The same things with other medicines, for example, if you take outdated Tylenol (acetaminophen) or Advil (ibuprofen) and feel no effect, most probably it already lost its properties. 
Note that you should discard any medicine that smells bad, looks odd (powderly or shattered), or dried up (creams), whether it expired or not.