Treacly (adjective)

1. Excessively sweet or sentimental.
2. Cloyingly sweet, overly sentimental, or saccharine.

Origin:

Mid 19th century: from treacle, alteration of syrup.

Examples:

1. The treacly love song made her feel nauseous.
2. The treacly romance novel was filled with cliches.
3. The treacly smile on his face made her suspect his sincerity.
4. The treacly tone of his voice was a clear indication that he was lying.
5. The treacly voice-over narration ruined the movie for her.