While there are apparent similarities, they are quite different in their history and the details of their doctrine. Like most moslem sects they are very complex to understand and even more difficult to summarize!
Alevis and Alawis have in common that , to a certain degree they consider themselves to be part of the wider Shi`a movement, who revere Ali (Muhammad’s cousin and son-in-law) and the Twelve Imams of his house (Ithna’shari).
According to Yaron Friedman, distinct Alawi/Alavi beliefs include the belief that prayers are not necessary, they don’t fast, nor perform pilgrimage, nor have specific places of worship.
1. Syrian Alawis are a prominent mystical and syncretic religious group centered in Syria who are often described as a branch of Shia Islam. The sect seems to have been organized by a follower of Muhammad ibn Nusayr, who died in Aleppo about 969. It has integrated doctrines from Ismaili Islam and Christianity ( i.e celebration of Chritsmas …).
A fatwa by Imam Musa al Sadr declares them Shi’a Muslims, that is Ithna’shari (Twelve Imams). He said: The Alawis are of the Shi’a and the Shi’a are of the Alawis. The most obvious difference between Alawites and Shi’ite Muslims, is that Alawis believe the Sunni Caliph and Shi’ite Imam Ali is an incarnation of one of the persons of God and wholly divine, along with Jesus Christ, The Prophet Muhammad and many other eastern holy men
2. Turkish Alevism’s origin is controversial. It goes back to Shah Ismail (founder of the Safavid dynasty in Azerbajian, Iran). His father Sheikh Haydar was part of a Sufi order and the leader of the growing Shia community in Azerbajian, the Qizilbash.
The Turkish Alevis ( originally called Qizilbashi ) have complex theological beliefs derived from Shiism but with some particularities, one of them is the belief of the unity of Allah, Mohammad and Ali. They also believe in the Twelve Imams but with a different interpretation of their symbols. They behave more like a Sufi order minus shari’a. There are many branches among them with different doctrines. Some go to Qom in Iran to study in Shia religious schools.